Three-dimensional (3D) video coding is developed for encoding or decoding video data of multiple views simultaneously captured by multiple cameras. Since all cameras capture the same scene for both the texture data and depth data, there is a large amount of redundancy between texture and depth data in the same view. According to HEVC, the coding process is applied to each block, named as coding unit (CU) and each CU is subject to prediction process. Each CU may be divided into one or more prediction units (PUs) and the prediction process, such as Intra or Inter prediction, is applied to each PU. To reduce the redundancy, a texture-partition-dependent depth partition is utilized for processing a current depth block collocated with a collocated texture CU at the same quad-tree level according to the current 3D-HEVC (3D video coding based on high efficiency video coding (HEVC)).
In order to simplify the texture-partition-dependent depth partition, limitation on the quad-tree based depth partition is imposed, which restricts the quad-tree for the depth partition no deeper than the quad-tree for the texture partition. Without this restriction, the depth partition may require too much coding time and may cause increased BD-rate, where BD-rate represents a rate-distortion performance measure often used for video coding. The texture-partition-dependent depth coding according to the conventional method is shown in FIG. 1, where a 2N×2N texture prediction unit (PU) can be partitioned into a 2N×2N, 2N×N, N×2N or N×N PU. However, when the texture PU is partitioned into 2N×2N, N×2N or 2N×N blocks, the corresponding depth partition size will be always 2N×2N as shown in FIG. 1.
While the quad-tree partition is always symmetric in the early HEVC development, asymmetric motion partition (AMP) was introduced into HEVC later. AMP partitions include 2N×nU, 2N×nD, nL×2N and nR×2N as shown in FIG. 2. According to the conventional 3D-HEVC, when the texture PU is partitioned into N×N blocks, the current texture-partition-dependent depth partition allows the depth block to be partitioned into any of the allowed candidate depth partitions as shown in FIG. 2. However, the 2N×2N partition is the only candidate depth partition for all other texture block sizes.
There are some issues with the conventional texture-partition-dependent depth partition. First, the original method was developed before AMP is utilized for motion partition in HEVC. Therefore, the partition distribution between texture and depth shown in FIG. 2 appears to be skewed, where a full candidate depth partition set is allowed for one texture partition (i.e., N×N) while a single candidate depth partition candidate (i.e., 2N×2N) is allowed for the rest of the texture partitions. Furthermore, the depth partition candidate is so limited (i.e., single 2N×2N candidate) for all texture partition sizes other than N×N, it may degrade the coding efficiency of the depth data and have negative impact on the quality of coded depth data. Consequently, coding tools such as VSP that rely on the reconstructed depth data may also be impacted to lower picture quality. Therefore, it is desirable to develop improved texture-partition-dependent depth partition to overcome these issues.